Ohhhhh Ohhhh O2 sensors can kiss my butt

[pife999]

I have a 93 325i and i replaced the o2 sensor and the light and code (1221) went away for a day. What could cause this light and code to come back on after only a day of running perfect. Any suggestions would be greatly appreciated. Thanks for all of your time.

[im]

i do not have the book for code 1221 but when an oxygen sensor triggers it does not mean that the sensor is bad 100% of the time...the triggering of the sensor may be do to a vacuum leak..many of the hoses around engine with a small vacuum leak could trigger an o2 sensor.
consider checking all hoses from air filter box to engine..and any hose that leaves the valve cover gasket to its final destination(passenger engine side to driver engine side) ...on an older car sometimes VACUUM hoses look ok to the eye but when you follow them sqeeze from start to finish...many times the hoses fall apart from inside out due to fumes + oil + gases etc..even a missing oil dip stick can cause a vacuum leak...old/ incorrect / loose gas cap can trigger the error codes.

[E36 Phantom]

A vacuum leak won't trigger an O2 code.

Sounds like a wiring problem, Pife.

[pife999]

Even with the o2 sensor being relaced it cleared the code?? thanks a lot for what has been suggested i would like even more input. thanks greatly

[whosyadadie01]

did you change the rite o2 sensor ?

[pife999]

there is only one on a pre obd2 car.
So yes

[whosyadadie01]

hm look at that ... whata surprise :yawn:

[Garyx5]

which octane of gas do you put into your car?

[E36 Phantom]

hm look at that ... whata surprise :yawn:

:dunno:

Confused. He's right, there is only one on OBDI ones.

[CJH]

A vacuum leak won't trigger an O2 code.

Sounds like a wiring problem, Pife.

Wrong, vacuum leak is one of the more common faults. It is infact one method to change the voltage produced by the O2 sensor. Variation of voltage outside acceptable range is the control signal for the ECU.

Wiring should be checked as part of the diagnosis.

Green wire = 12 volt + for O2 sensor heater from relay
Brown = heater ground
Yellow = O2 sensor output voltage +
Black = O2 sensor output voltage ground

[pife999]

do you know the resistance range on the sensor between the yellow and black?

[CJH]

No specs on resistance, better is a quick test of the voltage produced. Connect meter through the connector (with it still plugged together) If running lean, it will be approx 0.2 volts. Rich 0.8 volts. In reallity, it is a fluctuating voltage, to see it you really need an oscilloscope, or a digital voltmeter with an analog bar. In range, good bet it is a good sensor. To watch response, force a lean condition by disconnecting an injector or creating a vacuum leak, look for voltage to go low.

From technical bulletin:
The sensor can be tested for output by connecting to it a digital voltmeter, set to a 2v scale. Connect the +ve test lead to the sensor signal wire [See wire colours] and the -ve test lead to earth/battery -ve. The voltage produced should swing from app 0.2v to 0.8v and back around once per second. If the voltage is stuck high then the engine is probably running rich for some other reason. If stuck low then usually either a faulty Lambda Sensor, air leak or an engine running very weak for some reason.

[pife999]

Just ran a test with the old fluke and she's telling me the sensor is perfect. There was what i believe to be and air temp sensor hanging out of my plenum box so i reinstalled that also and the light dissappeared at high rmps when reving. I have the battery unhooked and i hope this will reset the odb1

[CJH]

You could have a good O2 sensor, but a fuel issue that's triggering it.
Defective fuel pressure regulator -running rich or lean,
leaks - lean,
weak fuel pump - lean at high rpm

Hope the reset cures it.

[pife999]

hears a little follow up. after unhooking the battery for several hours and restarting the car it still runs like total ****. it is running way to rich as there is deffinatly raw fuel being dumped out the exhaust. when i get the vanos to kick in the car screams to life. any more suggestions of possible problems would be great.